Sound stroboscope



July 13, 1943. ku Tz 2,324,305

scum) STROBOSCOPE Filed Jan. 30, 1941 SOUND 3 A MPL IF IE R I 30 Inventor: Lowell M. Kurtz,

l-lis Attorney.

Patented July 13, 1943 2,324,305 SOUND s'rnoBoscorE" Lowell M. Kurtz, Scotia, N. Y., assignor to General Electric Company, a corporation of New York Application January 30, 1941. Serial No. 376,605

4 Claims. (Cl. 88-14) My invention relates to stroboscopes and in particular to sound stroboscopic apparatus and its combination with a vision stroboscope, the two being synchronized, whereby a particular noise in an operating machine or the like may be localized and identified and the cause therefor ascertained and studied both visually and auditorially, simultaneously.

The features of my invention which are believed to be novel and patentable will be pointed out in the claims appended hereto. For a better understanding of my invention, reference is made in the following description to the accompanying drawing, in which Fig. i represents a perspective viewof one form of my invention pictured as employed for ascertaining the cause of a particular noise in a gear drive, Fig. 2 is a sound directing attachment that may be applied to the apparatus of Fig. 1, Fig. 3 represents a form of my invention where the noise under investigation is picked up by a microphone and amplified, and Fig. 4 represents a handle that may be used for the convenience in placing the noise pick-up microphone and stroboscope lamp in locations, access to which might otherwise be difficult.

Referring to Fig. 1, ill and ii represent machinery parts assumed to bein operation at high speed and in which there exists objectionable noise. In the example shown, the parts l and l l comprise a gear drive. Let it be assumed that these gears make a noise other than that usually made by well-fitted properly aligned gears and the cause thereof is not revealed by ordinary inspection when the gears are stationary. My stroboscope apparatus is represented as being used to ascertain the location of the defect or other cause of the objectionable noise and to study the gears while in motion at the instant the objectionable noise occurs.

The apparatus comprises a sound transmitting channefin the form of a tube comprising aligned sections 62 and it between which is interposed a rotary disk it. The two sections of the tube are secured together by a strap loop M. The free end of tube section i2 is held near the noise source and in the opposite end of tube section I3 is inserted a stethoscope device l5 by means of which sounds in the tube may be readily conveyed to the ears of the operator as represented. The disk M is shown driven by an electric motor it having a speed controller ll in its circuit l8 and by means of which the motor speed may be accurately varied. The sound tube is firmly supported to the motor frame by the support l9 so that the disk can be rotated between the closely using the same.

spaced tube sections but without rubbing against them. The supporting framework for the motor is preferably provided with a handle 20 by means of which the device may be carried about and held in any desired operating position with the speed regulator easily accessible to the operator Preferably combined with the motor is a tachometer 23 by means of which the speed of disk I4 is visible to the operator. The disk I4 is provided with an arcuate opening 211 of a radius such that this opening is aligned with the sound tube once per revolution of disk l4 and also large enough so that the operator in the position shown can look through this opening about the tube The peripheral length of the opening is preferably adjustable and for this purpose the disk is preferably made up of two disk sections clamped together on the motor shaft with willcient friction between them that they will remain in any relative position to which adjusted, but nevertheless so that they can be adjusted to vary the length of the opening and hence the period of interruption of the communicating channel. The disk sections are made of opaque material through which sound does not pass readily.

It is now seen that during that relatively short portion of a revolution of disk l4 when the opening therein is aligned with the sound tube, sound may be readily transmitted from section l2 to section l3 so that sounds adjacent the free end of the tube are efliciently transmitted to and heard by the operator but when the solid portion of the disk I4 is rotated between the sound tube sections, such sound transmission is very greatly reduced and is in effect interrupted over a larger portion of the period of revolution of the disk That is, the contrast between the two conditions is so great that the device is an effective interrupter of the ability of the channel to transmit sound. I have found it advisable to stretch thin flexible membranes over the opening 2| 9n the outer side of each disk section to provide smooth outer disk surfaces. This eliminates wind turbulence and noises incident thereto which would otherwise exist at high speeds of the disk due to the edges of the openings cutting through the air. On the other hand, the thin tight membranes efliciently transmit sounds between the tube sections. Such membranes are preferably transparent because the usefulness of this device is greatly increased by its simultaneous use as a visual as well as a sound stroboscope. I have found transparent Cellophane membranes to be suitable for my purposes and the edge of such a membrane is indicated by the line 22. The membranes may I of course extend over the entire sides of the disk sections but this is unnecessary.

In the tube section I3 I have indicated an adjustable damper by means of which the efiiciency of the sound transmitting medium may be reduced where that becomes desirable.

To explain the use of this device, let it be assumed that the gears shown at l and II make an unnecessary amount of noise, that the gears are rotating at such a high speed that the extra noise sounds like a steady roar to the unaided ear. If this extra noise is caused by an improperly cut tooth on gear H, for example, the noise will occur synchronously with the rotation of such gear. If the noise is due to something lodged between the teeth of gear ill or to an unbalancing of its shaft, such as to cause the gear ID to rotate eccentrically, the noise will occur synchronously with the rotation of gear l0. To determine the rate of vibration of the noise in such a case, the disk It is adjusted in speed until it is nearly synchronous with gear I I. This relationship occurs as soon as gear ll, observed through the visual stroboscope, appears to rotate forward or backward at a very slow rate.

The sound interrupter of course operates synchronously with the visual sight interrupter so that if the sound vibrations occur synchronously with the rotation of gear I I, the sound will grow louder and fade away as the stroboscopic image of the gear rotates. If this does not occur, the operator looks at the other gear l0 and adjusts the speed of disk l4 until nearly synchronous with gear ID. If the rate of vibration causing the noise is synchronous with either gear, this fact can quickly be ascertained and if found to be synchronous with gear ID, for example, the exact angular location of gear II! when such sound occurs will be observed through the stroboscope when looking at the point of mesh of gear in when the sound is the-loudest, assuming of course that the noise emanates from the point of gear mesh. This point can be identified by providing suitable markings on the gear as by having the teeth numbered.

Now the operator may adjust the speed of disk l4 and the period of interruption so as to drift back and forth through synchronism and in phase with the sound loudness, and he can observe the behavior of the tooth causing the noise and the adjacent teeth at the point of mesh as if nearly stationary at the instant the noise is produced and can note any peculiar behavior thereof, such for example, as a radial movement. Note that the operator can move his head considerably and look through the opening 2| at various angles without changing the position of tube i2l3 so that he can examine a considerable peripheral area of the rotating gear as if stationary or nearly so at the time it is causing the objectionable noise.

If the noise is caused by vibration at a particular speed of the stroboscope which is nonsynchronous with the speed of one of the gears, that fact can be ascertained also, the rate of vibration determined and the sound located and if any machine part has a sufficient amplitude of vibration at such rate to be observed visually, such movement can be seen through the visual stroboscope. In such a case the speed of disk ll is varied until the sound slowly grows loud and then fades away. This will occur when the stroboscope speed is nearly synchronous with the'noise rate, at which time the opening of the sound shutter drifts slowly through a condition where it is opened in phase with the sound pulsations. Then, by moving the sound receiving end of the sound tube about the point of loudest sound the probable source thereof can be located. The rate of sound vibration may be noted on the gauge 23 and if the vibrations cause visible movement of machine parts, such movement can be seen through the visual stroboscope.

I have found this device useful in reducing the noise made by valves of compressors, such as are used on household refrigerators, where nois reduction is important because the valves can be observed while in high speed operation and any noise made by them listened to and its exact cause ascertained without guess work, and the proper steps may then be taken to minimize the noise.

Various forms of sound transmitting tubular extensions may be attached to section l2 to best observe sounds 'at various angles and in locations difiicult of access. Fig. 2 represents a right angle elbow tubular section that may be slipped on the free end of tube section I! and when so mounted, turned so as to open in any direction at right angles to the axis of tube section l2.

The effectiveness of either form of stroboscope is materially increased by their simultaneous use because one may both see the cause of the noise and hear the result of the impact. It is of course necessary that the noise vibration rate be within the audible range which is generally between- 16 and 20,000 double vibrations per second.

In Fig. 3 I have diagrammatically represented a form of my invention where the sound transmitting channel is partially electrical and the sound may be amplified and the Visual stroboscope effect produced by a flashing light. In this case I make use of a; variable speed contactor driven by a variable speed motor 24 as the sound and light interrupter. The light device 25 is preferably of a type that will give a sharp flash when energized. It is energized in synchronism with the motor speed through a contactor 26 driven by the motor 24. The machine being observed is indicated at 21 and adjacent thereto is a sound microphone 28 connected to earphones 29 through amplifier apparatus 30. The earphone circuit is connected through a circuit close er 3| also driven by the motor 24. The contactors 26 and 3| are usually adjusted to close so that the stroboscopic visual impression of machine 21 reaches the eye of the observer at the same instant that any sound made thereby at the instant of vision, reaches the ear of the observer. This may require a slight out-of-phase position of the two contact devices due to unequal lag in. the sound transmission system or in the light flashing system. I also preferably provide a tachometer 32 to indicate the motor speed and a controller 33 for varying the speed of the motor. The microphone and lamp may be independently adjustable about the machine to be studied as indicated in Fig. 3, or they may be mounted on a handle 35 as shown in Fig. 4 for ease in simultaneous adjustment by the operator in and about the machine.

In Fig. 4 the handle may have a universal joint 36 to facilitate adjustability, and the microphone 28 may be hinged to a strap 31 frictionally rotat be obtained with the flashing lamp form of of the way as much. as possible. Best visual stroboscopic eifect will of which the degree of amplification at any given frequency may be adjusted and a knob for this purpose is represented at 3B. The relative duration of closure of the circuits of the sound and light stroboscopesfmay be adjusted by'moving their contacts 30 and 26 toward and away from their operating cams and the time relation of closure may be adjusted by moving the contactsabout the motor-driven cam shaft.

In accordance with the provisions of the patent statutes, I have described the principle of operation of my invention together with the apparatus which I now consider to represent the best embodiment thereof, but I desire to have it understood that the apparatus shown is only illustrative and that the invention may be carrie out by other means.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A combined visual and audible stroboscope apparatus comprising a sound communicating channel and a visual communicating channel adapted for simultaneous audible and visual investigation of the same object, and means for simultaneously and intermittently interrupting both of said channels, the periods of interruption section of good sound transmitting characteristics and an opaque section of poor sound transmitting characteristics, means for rotating said disk through said slot so as to alternately move said different disk sections therethrough to intermittently effect interruptions in the tubular sound communicating channel, said transparent'disk section being of such dimensions as compared to the tubular channel as to permit a person to look through the transparent section about the channel when the transparent disk section is passing through said channel.

3. In a stroboscope, a combined vision and sound interrupter comprising a rotary disk of opaque material having poor sound transmitting characteristics and an arcuate opening therein covered on both sides with a transparent membrane.

4. A sound stroboscope comprising a tubular sound communicating channel containing a slot, 2. disk mounted for rotation through said slot, said disk having a relatively small section of good sound transmitting characteristics and a relatively large section of poor sound transmitting characteristics, means for rotating said disk in said slot so as to alternately move said disk sections therethrough to intermittently effect interruptions in the sound communicating channel, means for driving said disk at different speeds to vary the frequency of such interruptions and stethoscope means to facilitate detection of .sounds transmitted through said channel.

LOWELL, M. KURTZ. 

